1. Field of the Invention
The present invention relates to a photosensitive resin composition, insulating film, and process for forming the film, more particularly relates to an imide-based photosensitive resin composition suitable for a high density flexible wiring board, able to be alkali developed, able to be cured at a low temperature, and giving a film low in elastic modulus and superior in flex resistance and chemical resistance, a pre-baked film, an insulating film and a process for formation of the same.
The photosensitive resin composition of the present invention is suitable as a material for formation of a coating material for a COF (chip on flexible printed board), BGA (ball grid array), CSP (chip scale package), or other flexible wiring board or a material for forming an interlayer insulating film, a protective film for a circuit, a protective film for a semiconductor element, and a passivation film.
2. Description of the Related Art
A material for formation of a coating material for a COF, BGA, CSP, or other flexible wiring board, an interlayer insulating film, a protective film for a semiconductor integrated circuit, a protective film for a semiconductor element, a passivation film, etc. is required to have an excellent heat resistance and insulation property. A photosensitive heat resistant material is sought due to the requirements for higher density and higher integration. Further, various polyimides having a high insulation property and heat resistance have been proposed.
For example, known in the art is a method of coating a polyimide resin on the entire surface of a device substrate, partially protecting the surface with a photoresist, and etching the polyimide resin film by hydrazine etc., that is, an alkali etching method.
In this method, however, the steps are complicated. Further, it is necessary to use highly toxic hydrazine or another strong alkali aqueous solution as an etching solution.
Alternatively, an etching method using an organic solvent as a developing agent has been proposed for a photosensitive polyimide-based resin, for example, a precursor of a polyimide resin, that is, a polyamic acid, in which a photopolymerizable acryloyl group is introduced at an ester bond (Japanese Examined Patent Publication (Kokoku) No. 55-30207, Japanese Examined Patent Publication (Kokoku) No. 55-341422, etc.) or in which an acryloyl group is introduced in an amic acid at a salt structure (Japanese Examined Patent Publication (Kokoku) No. 59-52822 etc.)
Further, alkali developing type photosensitive polyimides are being developed. For example, a photosensitive polyimide obtained from a positive type polymer comprised of a polyamic acid having naphthoquinone diazide introduced at a carboxyl group (Japanese Unexamined Patent Publication (Kokai) No. 6-258835) and a negative type photosensitive polyimide comprised of a polyamic acid having a photopolymerizable acryloyl group introduced at an ester bond and further having a carboxyl group etc. introduced into the side chain to make the polyamic acid soluble in a basic aqueous solution (Japanese Unexamined Patent Publication (Kokai) No. 10-95848) have been proposed.
These photosensitive polyimide resins, however, require high temperature heating of over 350xc2x0 C. for post-baking, so there are the problems of a detrimental effect on the dimensional stability of the board and a low heat resistance or chemical resistance (acid resistance, alkali resistance, solvent resistance, etc.) of the obtained insulating film.
An object of the present invention is to provide an imide-based photosensitive resin composition having an imide-based resin which is soluble in an organic solvent, not requiring high temperature post-baking, having an imide-based resin which is photosensitive and can be developed even by a weak alkali aqueous solution, and giving an insulating film by post-baking which has heat resistance, chemical resistance (alkali resistance, acid resistance), and a high insulation property, such an insulating film, and a process for forming such an insulating film.
According to a first aspect of the invention, there is provided an imide-based photosensitive resin composition comprised of (1) a photosensitive imidosiloxane oligomer comprised of a reaction product of an imidosiloxane oligomer having a functional group reactive with an epoxy group obtained by reacting a total of diamines of 70 to 90 mol % from 10 to 50 mol % of an aromatic diamine having a functional group reactive with an epoxy group, 10 to 70 mol % of diaminopolysiloxane, and 0 to 20 mol % of an aromatic diamine having plural benzene rings, with respect to 100 mol % of a tetracarboxylic dianhydride and an epoxy compound having a photosensitive group, (2) an isocyanate having an unsaturated bond, (3) a photopolymerization initiator, and (4) an organic solvent, wherein the ratio of the components is 1 to 80 parts by weight of the (2) isocyanate having an unsaturated bond and 0.01 to 30 parts by weight of the (3) photopolymerization initiator with respect to 100 parts by weight of the (1) photosensitive imidosiloxane oligomer.
According to a second aspect of the invention, there is provided a pre-baked film of the imide-based photosensitive resin composition coated on a support.
According to a third aspect of the invention, there is provided an insulating film obtained by coating an imide-based photosensitive resin composition on a substrate, then prebaking it to form a thin film, exposing it, alkali developing it, then post-baking it to obtain a cured film.
According to a fourth aspect of the invention, there is provided a process for forming an insulating film comprising coating an imide-based photosensitive resin composition on a substrate, then prebaking it to form a thin film, exposing it, alkali developing it, then post-baking it.
According to a fifth aspect of the invention, there is provided a process for forming an insulating film comprising laminating a dry film of a photosensitive resin composition containing a resin component containing a reactive group in a molecule and a monomer having reactivity with a reactive group on a substrate, alkali developing it, and then post-baking it at not more than 250xc2x0 C., wherein the insulating film has an elastic modulus of not less than 5 kgf/mm2 and not more than 100 kgf/mm2, an elongation rate of not less than 5%, and alkali resistance.